The Keele - Exeter young cluster survey : I . Low mass pre - main sequence stars in NGC 2169

We have used RCIC CCD photometry from the Isaac Newton telescope and intermediate resolution spectroscopy from the Gemini North telescope to identify and characterise low-mass (0.15 < M/M⊙ < 1.3) pre-main sequence stars in the young open cluster NGC 2169. Isochrone fitting to the highand low-mass populations yields an intrinsic distance modulus of 10.13 −0.09 mag and a model-dependent age of 9±2Myr. Compared with the nearby, kinematically defined groups of a similar age, NGC 2169 has a large low-mass population which potentially offers a more precise statistical investigation of several aspects of star formation and early stellar evolution. By modelling the distribution of low-mass stars in the IC versus RC −IC diagram we find that any age spread among cluster members has a Gaussian full width at half maximum 6 2.5Myr. A young age and small age spread (< 10Myr) are supported by the lack of significant lithium depletion in the vast majority of cluster members. There is no clear evidence for accretion or warm circumstellar dust in the low-mass members of NGC 2169, bolstering the idea that strong accretion has ceased and inner discs have dispersed in almost all low-mass stars by ages of 10Myr.